Conventionally, for example, the following nitride phosphors have been known. These nitride phosphors can be excited with ultraviolet light-near-ultraviolet light-violet light-blue light, and emit visible light in a warm color having an emission peak in a wavelength range of 580 nm to less than 660 nm. Therefore, these nitride phosphors also have been known to be suitable for a light-emitting device such as a white LED light source.
(1) M2Si5N8:Eu2+ (see JP 2003-515665 A)
(2) MSi7N10:Eu2+ (see JP 2003-515665 A)
(3) M2Si5N8:Ce3+ (see JP 2002-322474 A)
(4) Ca1.5Al3Si9N16:Ce3+ (see JP 2003-203504 A)
(5) Ca1.5Al3Si9N16:Eu2+ (see JP 2003-124527 A)
(6) CaAl2Si10N16:Eu2+ (see JP 2003-124527 A)
(7) Sr1.5Al3Si9N16:Eu2+ (see JP 2003-124527 A)
(8) MSi3N5:Eu2+ (see JP 2003-206481 A)
(9) M2Si4N7:Eu2+ (see JP 2003-206481 A)
(10) CaSi6AlON9:Eu2+ (see JP 2003-206481A)
(11) Sr2Si4AlON7:Eu2+ (see JP 2003-206481A)
(12) CaSiN2:Eu2+ (see S.S. Lee, S. Lim, S.S. Sun and J.F. Wager, Proceedings of SPIE—the International Society for Optical Engineering, Vol. 3241 (1997), pp. 75-83)
In the above phosphors, “M” represents at least one alkaline-earth metal element (Mg, Ca, Sr, Ba), or zinc (Zn).
Conventionally, such nitride phosphors have been produced mainly by the following production method: a nitride of the element “M” or metal, and a nitride of silicon and/or a nitride of aluminum are used as materials for a phosphor host, and they are allowed to react with a compound containing an element that forms a luminescent center ion in a nitriding gas atmosphere. Furthermore, a conventional light-emitting device has been configured using such a nitride phosphor.
However, because the request for the above-mentioned light-emitting device is being diversified year after year, there is a demand for a novel phosphor different from the above-mentioned conventional nitride phosphor. In particular, there is a great demand for a light-emitting device containing a large amount of the above-mentioned light-emitting component in a warm color, above all, a red light-emitting component, and there is a strong demand for the development of such a light-emitting device. However, actually, only a small number of phosphor ingredients are available, so that there is a need for developing a novel phosphor ingredient and a novel light-emitting device containing a large amount of light-emitting component in a warm color.
Furthermore, according to the conventional method for producing a nitride phosphor, it is difficult to obtain and produce a high-purity material, and a nitride phosphor is produced using, as a main material, a nitride of alkaline-earth metal, alkaline-earth metal, or the like, which is difficult to handle in the atmosphere due to its chemical instability. Therefore, it is difficult to mass-produce a high-purity phosphor, reducing the production yield, which increases the cost of a phosphor.
Furthermore, in the conventional light-emitting device, there is only a small number of kinds of applicable phosphor ingredients. Therefore, there is no room for selecting a material, and a manufacturer that supplies a phosphor is limited. Consequently, a light-emitting device becomes expensive. Furthermore, there is a small number of kinds of inexpensive light-emitting devices with a high emission intensity of a light-emitting component in a warm color (in particular, red) and with a large special color rendering index R9.
The present invention has been achieved in order to solve the above-mentioned problems, and its object is to provide a novel phosphor composition capable of emitting light in a warm color, in particular, a phosphor composition emitting red light. Another object of the present invention is to provide a method for producing a phosphor composition that can be produced at a low cost, suitable for mass-production of the nitride phosphor composition according to the present invention. Still another object of the present invention is to provide an inexpensive light-emitting device with a high emission intensity of a light-emitting component in a warm color (in particular, red) and with a large special color rendering index R9.
Regarding the technique of measuring the internal quantum efficiency and the external quantum efficiency of a phosphor according to the present invention, a technique capable of conducting measurement with high precision already has been established. Regarding a part of phosphors for a fluorescent lamp, absolute values of the internal quantum efficiency and the external quantum efficiency under the irradiation of light (excitation with ultraviolet light of 254 nm) with a particular excitation wavelength are known (e.g., see “Publication of Illuminating Engineering Institute of Japan” by Kazuaki Ohkubo et at, 1999, Vol. 83, No. 2, p. 87).